Decimeter wave transmitter



Allg.l 25, 1942. K CHRIST 2,294,073

DECIMETER WAVE TRANSMITTERv Filed Dec. l5, 1939 /fzf/ @mi v v Patented Aug. 25, 1942 DEciMETEn WAVE TRANSMITTER Karl Christ, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof,

Germany, a company Application December 15, lssaserial No. 309,353

In Germany December 9, 1938 1 Claim. (Cl. 179-1715) This invention relates to the modulation of the frequency in decimeter wave transmitters connected in feed-back, the feed-back connection being preferably of the so-called three-point or cathode-point type.

As is well known, the frequency in generators of this kind maybe varied by varying the anode voltage. By varying the anode voltage in the rhythm of a modulating voltage a frequency' modulation is obtained. Such variation, however, also results in varying the high frequency energy and thus entails the disadvantage that in addition to the desired frequency modulation an undesirable amplitude modulation takes place.

In this regard, both the frequency and the high frequency amplitude will. be increasing in their turn. Apart from this it is known that a frequency modulation may be obtained also by'varying the grid bias periodically while keeping the anode voltage constant. Also in this casein addition to the desired frequency modulation an undesired amplitude modulation results. This phenomenon, however, is the reverse of that which occurs in the event of an anode voltage modulation, because on varying the grid bias in the positive sense the frequency will decrease while the amplitude will be increasing.

The present invention aims to suppress such undesired amplitude modulation. For this purpose grid bias and anode voltage are varied in the rhythm of the modulating voltage both at the same time and in such mutual relation that the highv frequency energy shall vremain constant. If in this way the anode and grid voltages are varied in the requisite manner the advantage results that there will be a somewhat great frequency variation which is practically linear in relation to the voltage variations, that is to say, is proportional to these. An undesirable amplitude modulation will not occur here. In the accompanying drawing, Figs. 1, 2, 3 are diagrams each showing one embodiment of the invention. Fig. 1 illustrates a modulating voltage coupled to a transmitting tubeA by means of a potentiometer; Fig. 2 illustrates a modulating 'voltage coupled to a transmitting tube by means of transformers; and Fig. 3 illustrates a modu lating voltage coupled t`o the grid of a trans- Y mitting tube and a resistor in 'the anode circuit of the tube for regulating the anode voltage thereof in accordance -with variations in the modulating voltage. y

The arrangement represented in Fig. 1 has an electronic transmititng tube l the circuit arthree-point connection. The modulating voltage U is supplied at terminals 2, 3 over a potentiometer 4 in a manner to affect anode voltage and grid voltage both at the same time. A battery 5 in the anode circuit A serves as anode voltage source. By means of taps 6, 1 the ratio between anode voltage variation and grid voltage variation can be so adjusted that the high frequency amplitude remains constant. In

the grid circuit G a choke coil 8 and a resistance 9 are included, which however are immaterial to the idea of the invention.

The arrangement according to Fig. 2 is based on the principle involved in the arrangement shown in Fig. 1, with the difference that thex modulating voltage U is impressed upon the anode circuit A and the grid circuit G over transformers l0, il.

When adjusting the anode and grid voltages in this way the anode current will decrease with increasing voltage (negative resistance). Only the grid current rises with increasing grid voltage (positive resistance). A further advantage of the novel arrangement therefore is that the modulating energy may be very small.

Fig. 3 discloses means for effecting the invention in a manner diiierent vfrom the mode of opeartion peculiar to the arrangements illus` trated in Figs. 1 and 2.

When controlling the grid bias of the tube I while the anode 'voltage is kept constant the anode current varies in linear relation to the grid voltage. Accordingly, in the arrangement shown in Fig. 3 the modulating voltage is conveyed only to the grid circuit of the tube. 'I'he anode circuit contains an ohmic resistance R. By the anode current variationv due to the modulation effected in the grid circuit theranode voltage is automatically varied l at the same time.' 'I'he amount of 'such variation of the anode voltage depends upon resistance R and is so chosen, by

suitably calculating this resistance, that the high frequency amplitude remains constant. The arrangement according to Fig. 3 hence has the advantage that the modulating voltage need only be supplied to the grid circuit and that'the concurrent anode voltage variation, which acts to suppress an undesired amplitude modulation, 'is effected automatically. The requisite modulating energy is here very small.

The vnovel arrangement will be useful in many It is suitable not only for the modulation of transmitters but also for the purpose of respects.

frequency control. For instance, an automatic rangement of which is of the type known as sharp tuning of a heterodyne receiver may be ator an oscillator constructed in accordance with the invention. From the output circuit of auch receiver a regulating voltage is taken and this voltage is made to control the oscillator by acting on vboth the grid circuit and anode circuit at the same time.

What is claimed is:

A circuit arrangement for producing frequency modulated decimeter waves comprising an elec' tronic oscillator having a grid circuit and an obtained by employing as heterodyning generfrequency'uf the output energy of said oscillator 'comprisingilrst andreoond transformers, the

secondary windings of said transformers beim l. respectively connected in said grid and anode anode circuitl means for feeding energy from said anode circuit to said grid circuit, a source of modulating energy, and means for varying the circuits and the primary windings of said transformera being connected in sexies across said source of modulating voltage. the phase and magnitude o! the voltages fed to said grid and anode circuits over said transformers being so adjusted that the amplitude of the output ener'gy of said oscillator remains substantially constant at a predetermined value.

KARLCHRIST. 

